The present invention generally relates to magnetic heads, and more particularly to a magnetic head employed in a magnetic disc recording and/or reproducing apparatus such as a floppy disc drive.
For example, a magnetic head 1 having a construction shown in FIG. 1 and a magnetic head 2 having a construction shown in FIG. 2 are generally known magnetic heads which are employed in a magnetic disc recording and/or reproducing apparatus (hereinafter simply referred to as a magnetic disc apparatus).
The magnetic head 1 has sliders 3 and 4 made of a ceramic material and a magnetic head part 5 having a ferrite core. The magnetic head part 5 is indicated with a dot pattern and the illustration of a gap is omitted. The magnetic head part 5 is sandwiched between the sliders 3 and 4 and adhered together by an adhesive agent. In addition, a sliding contact surface 6 which makes sliding contact with a magnetic disc is formed by lapping a surface of the adhered structure to a mirror surface, and corner portions of the adhered structure are chamfered.
On the other hand, the magnetic head 2 has a magnetic head part 7 and a slider 8 which is located on only one side of the magnetic head part 7.
The magnetic heads 1 and 2 are respectively mounted on a head carriage (not shown) through a gimbal spring 9 as shown in FIGS. 3 and 2. FIG. 3 shows the magnetic head 1 in use, where two identical magnetic heads 1 confront each other through a magnetic disc 10 so that the magnetic heads 1 can record and/or reproduce information on respective sides of the magnetic disc 10 by making sliding contact with the respective sides. FIG. 2 shows the magnetic head 2 in use, where two identical magnetic heads 2 similarly confront each other through the magnetic disc 10. In FIG. 2, one magnetic head 2 and the magnetic disc are shown in phantom lines. As shown in FIGS. 3 and 2, the magnetic heads 1 and 2 respectively have a back bar 11 and a coil 12 coupled to the respective magnetic head parts 5 and 7.
But the magnetic head 1 suffers a problem in that satisfactory recording and reproducing characteristics cannot be obtained especially when a high density recording and reproduction are carried out, and an explanation will be given hereunder of this problem.
That is, the adhesive agent used to adhere the sliders 3 and 4 and the magnetic head part 5 of the magnetic head 1 is an epoxy adhesive agent in most cases. The epoxy adhesive agent is generally used because it is inexpensive and its thermosetting adherence occurs at a relatively low temperature. For this reason, it is not only possible to reduce the production cost but also reduce the undesirable effects caused by the difference between the thermal expansions of the magnetic head part 5 and the sliders 3 and 4. In addition, it has been considered in the past that the magnetic head 1 is satisfactory for use in the conventional magnetic recording and reproduction process in which the recording density is not extremely high.
However, the present inventors have found that a step d actually exists between the magnetic head part 5 and the sliders 3 and 4 as shown in FIG. 4. This fact was confirmed by measuring the smoothness of the sliding contact surface 6 of the magnetic head 1 with a high magnification by use of a measuring instrument such as TALYSURF 6 manufactured by Rank Taylor Hobson Ltd. of England and SURFCOM 900A manufactured by Tokyo Seimitsu of Japan. It is regarded that this step d is generated during a thermal process which is carried out in an adhesion step of the production process, during a processing step using a working solution carried out after the adhesion step, and due to an environment (for example, high humidity and temperature conditions of summer) in the process of forwarding and transporting the produced magnetic head 1. Further, it is regarded that this step d is also generated due to a difference in lapped quantities of the magnetic head part 5 and the sliders 3 and 4 caused by the different materials used therefor during a lapping process in which the sliding contact surface 6 is formed to the mirror surface.
A relation between the step d and the characteristics of the magnetic head 1 will now be considered. The magnetic head 1 is separated from the magnetic disc 10 by the existence of the step d, and a separation loss Ls can be described by the following formula, where d1 denotes a depth (micron) of the step d and W1 denotes a recording wavelength (micron). EQU Ls=54.6.times.(d1/W1) (dB)
It may be seen from the above formula that the separation loss Ls increases as the depth d1 increases and also as the recording wavelength W1 decreases, that is, as the recording density increases. The following Table shows the relation between the step d and the characteristics of the magnetic head 1 obtained by the present inventors for a case where d1=0.1 (micron).
TABLE ______________________________________ Recording Density Recording Wavelength Separation Loss (Bit Per Inch) (Micron) (dB) ______________________________________ 8717 5.83 0.94 34868 1.46 3.74 ______________________________________
As shown in the above Table, the separation loss is 0.94 (dB) and low when the recording density is 8718 (BPI) which is relatively low and the recording wavelength is 5.83 (microns) which is relatively large. Accordingly, there is virtually no undesirable effect on the magnetic recording and reproducing characteristics even when the magnetic head 1 has the step d of d1 =0.3 (micron).
However, when the recording density is 34868 (BPI) and the recording wavelength is 1.46 (microns) to carry out the high density recording (short wavelength recording), the separation loss becomes 3.74 (dB). Hence, although d1=0.2 (micron), the effect of the step d is large in this case and it is impossible to obtain satisfactory magnetic recording and reproducing characteristics.
In other words, the diameter of the magnetic disc has become smaller in recent years from the 8-inch disc, the 5-inch disc to the 3.5-inch disc, and the maximum recording frequency is inevitably reduced in order to achieve the high density recording with the given size of magnetic disc. For this reason, as the size of the magnetic disc is further reduced, the step d which conventionally did not cause any problems becomes the source of the deteriorated magnetic recording and reproducing characteristics.
On the other hand, the magnetic head 2 has a poor stability with respect to the gimbal spring 9 and the recording and reproducing characteristics are deteriorated thereby. Furthermore, the magnetic head 2 cannot be assembled with a high efficiency as will be described hereunder.
As shown in FIG. 2, the magnetic head 2 is mounted on the gimbal spring 9 by adhering the slider 8 on the gimbal spring 9 by an adhesive agent A indicated by a hatching. But according to this structure, the lower magnetic head 2 receives a clockwise moment of force as indicated by an arrow M and undergoes a rotary displacement when a load force P is applied in a direction of the arrow. The magnetic head part 7 can no longer make sliding contact with the magnetic disc 10 when this rotary displacement of the magnetic head 2 occurs, and the magnetic head 2 cannot accurately trace an intended track of the magnetic disc 10. In an extreme case, the magnetic head 2 separates from the magnetic disc 10 and there is a problem in that satisfactory recording and reproduction cannot be carried out. The upper magnetic head 2 suffers the same deficiencies as the lower magnetic head 2.
In addition, when mounting the lower magnetic head 2 on the gimbal spring 9, for example, the magnetic head 2 does not sit still in an upright position and rolls to the right in FIG. 2 due to the structure of the magnetic head 2. Therefore, the magnetic head 2 must be secured in position by use of an instrument or the like until the adhesive agent A sets or hardens, and the assembling of the magnetic head 2 cannot be carried out with a high efficiency.